How should we do if the drill tools buried or stuck during the construction of large-diameter pile foundations with rotary drilling rigs?

During the installation of large-diameter pile foundations by rotary drilling machines, accidents of hole collapse, buried drills, and stuck drills often occur. However, the causes, accident conditions, and on-site conditions of rotary drilling machine accidents are different, so the measures shoule be taken are also different. Sometimes, several treatment methods may be required. This article focuses on the treatment methods of buried drills and describes the treatment tools in detail for your reference.

After a buried drill or stuck drill accident occurs, the mud performance should be adjusted in time to control the further expansion of the accident, and the cause should be analyzed in time to take corresponding measures to avoid missing the best treatment opportunity. The treatment of buried drills can be summarized into methods and steps such as "clearing, penetration, blasting, expansion, fishing, smashing, and digging".

1. Treatment of sediment

"Clearing" means cleaning slag and washing holes. Slag cleaning can be carried out by positive and reverse circulation, high-pressure spraying, or using a well washing pipe air compressor. Slag cleaning should determine the mud quality and the hole cleaning equipment used according to the formation to avoid secondary hole collapse accidents during the drilling process. Use an air compressor to wash the hole.

2. Salvage of kelly bar and drill tool

(1) In some cases, the key to handling buried drilling accidents is to clear the passage between the bottom of the hole and the upper part of the drill tool, so that the bottom and upper parts of the drill tool form a communicating vessel to avoid the piston effect, which is called "penetration". In order to form a communicating vessel, several holes deeper than the accident hole are usually drilled on the side of the hole, and high-pressure rotary jetting is used for swing jetting. For passage formation, the power head is rotated and the main rope lifting force is increased at the same time, which may lift the kelly bar and drill tool together. Some treatment schemes use a combination of reverse circulation drilling rigs and reaming drill tools.

(2) "Explosion" means blasting the bottom of the hole. If the drill tool cannot be lifted after washing the hole, the drill tool can be destroyed by positioning blasting with explosives and the kelly bar can be lifted out. Generally, the foundation pile holes that use this method to handle accidents are close to the design depth, and can meet the bearing capacity requirements after design verification. After blasting, they can be directly poured.

(3) "Expansion" means using an reaming drill tool that is about 10 cm larger than the drill tool to expand the hole to below the drill tool gate, and then salvage the kelly bar and drill tool. The hole-reamer drill tool can be modified with a casing that is 10 cm smaller than the original casing diameter.

(4) The drill tool or kelly bar of the rotary drilling rig can be salvaged by the "sleeve, clamp, and hook" method. If the kelly bar is broken inside and the kelly bar and drill bucket are left in the hole, a diver can be sent to sleeve the kelly bar and drilling tools after the hole is expanded and cleaned. When the burial depth is shallow, the kelly bar can also be sleeved with a steel support. If the burial depth is deep, the kelly bar can be salvaged after the hole is expanded and the sediment is cleaned. If the sediment is thick, a sleeve can also be made. The lifting device is fixed to the three-section kelly bar with a homemade steel pin, and the pot-bottom-shaped salvage device is also fixed to the same section of the kelly bar. The straight wall height of the salvage device should be greater than the height of the drill tool to ensure that the wire rope welded inside it can clear the slag in place. When clearing the slag, the wire rope sleeve can be fixed on the power head to ensure that the rope sleeve is synchronized with the kelly bar.

When the drill tool is buried shallowly, you can also use the force of the hook to test it. Use a welded rigid rod to directly drill down and hook the crossbeam of the buried drill bucket to pull out the drill tool.

(5) If the depth after blasting cannot meet the requirements or the drill tool is broken in the hole, you can use an impact drill to smash the damaged drill tool and perform impact drilling into the final hole.

(6) In some areas, the water level is deep and the kelly bar is buried shallowly. The buried drill can be handled by digging manually. The size of the manually dug hole should be about 20 cm larger than the hole diameter. Finally, the Luoyang shovel can be used to hollow out the circle around the drill tool so that the drill tool can be dug out smoothly.

3. Measures to prevent stuck drill

(1) Check the drill bucket regularly and perform maintenance, especially when the gap between the bucket bottom and the hook increases. After drilling, the weight of the bucket bottom is supported by the bottom of the hole, which makes the hook easily pushed or shaken open by the debris.

(2) After closing the bucket bottom, use the main reel to shake or rotate left and right to impact the drill bucket. If the bucket door can be frequently shaken open, it means that the hook is not firm. Check the cause and repair it in time to avoid the bucket bottom being shaken open when drilling into a geology with large vibration.

(3) If drilling into a stratum with large vibration, low speed and light pressure should be used to reduce vibration. When drilling into a hard stratum, pay attention to the wear of the drill bucket and replace the side teeth in time to avoid shrinkage.

(4) When lifting the main reel, the lifting speed slows down because the load can change the sound of the main reel, and the mast will sink after the load increases. By listening and watching, you can know the load change in the first time and change the operation in time.

(5) If the lifting load increases, you should slow down or stop lifting the main reel. The depth and geological conditions of the drill bucket can be known through the depth meter display. At the same time, you can also rotate the kelly bar at a low speed to see if there is a load, so as to know whether the bucket bottom is open.

(6) Even if you are sure that the bucket bottom has been opened, you should remain calm, reduce the engine speed to the minimum, lift the main reel through the output of low flow and low torque, feel the load by listening, stop lifting immediately once the load increases, rotate in place and use the open bucket bottom to expand the hole. If the expansion load increases, you should reverse or lower the main reel and continue to expand the hole to prevent it from getting stuck.

(7) When the bucket bottom is opened, you must know the geological conditions at the depth. For example, the bucket bottom is opened in the pebble layer at a depth of 35 meters, and above 30 is all mud layer, so you only need to insist on lifting 5 meters to eliminate the danger.

(8) Whether the friction type or the machine lock type kelly bar is used, the fall of the kelly bar caused by the rod has a great impact force. If this impact force falls on the kelly bar tray, it will shake the bucket door open.

(9) After the drill bucket is stuck, first use the measuring rope to slowly test the condition of the drill bucket, whether there is slag in the bucket, whether the bucket bottom is open, if it is determined that the bucket bottom is not open, it should be a clamped drill.

(10) Avoid hard drilling and hard lifting to prevent the main winding wire rope from being pulled off and the kelly bar from being twisted off, which will lead to the loss of the best solution opportunity and huge losses.

(11) It takes a certain amount of time to deal with the stuck drill, so the mud viscosity and water pressure should be maintained to prevent the hole from collapsing and protect the drilling rig.

(12) Even if it is stuck, there are good solutions. If you are not sure about the cause and have no experience in handling it, please do not act rashly.

Last but not least, it's very important to choose quality and suitable drilling tools. Drillmaster Group has 15 years experience on pile foundation field. Experienced sales and engineers provide all-in-one solution. Welcome to contact us if any needs.